The Effects Of Casting Temperature And Humidity On The Structure And Performance Of Fixed Carrier Composite Membrane For CO₂ Separation

The fixed carrier membranes for CO2 separation are very attractive due to itshigh permselectivity as well as good stability. In this paper, the effects of castingtemperature and humidity on the structure and performance of fixed carriermembrane for CO2 separation were studied in detail. Polyvinylamine(PVAm) is a kind of fixed carrier membrane for CO2 separation,which has been developed by our group. The fixed carrier composite membraneswere prepared with PVAm as separation layer and polyethersulfone(PES)ultrafiltration membrane as substrate by using dip-coating process. The membranepreparation condition was controlled by using Artificial Climate Chamber.XRD(X-ray diffractions)and ESEM(Environmental Scanning Electron microscope)were employed to characterize the microstructure of the composite membranes. Withthe decrease of humidity of preparation environment the crsytalinity of themembranes decreases, and the aggregate structure of the membranes become looser.The permselectivities of composite membranes prepared at different humidity weremeasured with pure CO2 and CH4 as well as binary mixture of CO2 and CH4. Theresults show that both CO2 permeation rate and selectivity of CO2 over CH4 havemaximums with the reduce of humidity. The membrane prepared at 30℃ andRH40% displays the highest CO2 permeation rate and selectivity. For pure feed gases,at pressure of 109cmHg, the membrane displays a CO2 permeation rate of 4.6×10-6cm3(STP)/cm2.s.cmHg and CO2 /CH4 ideal separation factor of 85. For mixedfeed gas composed of 50vol% CO2 and 50vol% CH4, at feed pressure of 109cmHg,the membrane has a CO2 permeation rate of 4.4 ×10-6cm3(STP)/cm2.s.cmHg andCO2 /CH4 separation factor of 42. The separation of CO2 from N2 and O2 was alsoinvestigated in this study. PVAm/PS composite hollow fiber membranes were developed with PVAm asseparation layer and polysulfone(PS) ultrafiltration hollow fiber membrane assubstrate. The effect of preparation condition on the membrane performance wasinvestigated. The results show that the membrane prepared in Artificial ClimateChamber(T=30℃, RH=40%) displays better permselectivity and reproducibility thanthe membrane prepared in room environment(T=20~25℃, RH=40~65%). Blend composite membranes were developed with the blend of PVAm andpolyethylene oxide( PVAm+PEG) as separation layer and PES ultrafiltration IImembrane as substrate. XRD was employed to investigate the effect of PEG contenton crystalinity of the blend composite membranes. The results show that thecrystalinity of the blend membranes has a minimum with the increase of PEG content.The blend membrane with PEG content of 10wt% displays excellent comprehensiveperformances. For pure feed gas, at pressure of 96cmHg, the membrane displays aCO2 permeation rate of 5.7×10-6cm3(STP)/cm2.s.cmHg and CO2/CH4 ideal separationfactor of 65. For mixed feed gas composed of 50vol% CO2 and 50vol% CH4, at feedpressure of 100cmHg, the blend membrane has a CO2 permeation rate of 7.0×10-6cm3(STP)/cm2.s.cmHg and CO2 /CH4 separation factor of 32.